Compositions containing vinylidene fluoride polymers which are stabilized to heat

ABSTRACT

The compositions contain, as heat stabilizer, an effective amount of bismuth carboxylate chosen from bismuth succinate, acrylate and terephthalate and their mixtures. In general, this amount is at least 0.05 part and does not exceed 5 parts per 100 parts by weight of vinylidene fluoride polymer. 
     The heat stabilizers according to the invention are suitable both for the thermal stabilization of virgin polymers and for the stabilization/decoloration of thermally degraded waste polymers.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a continuation application of pending U.S.application Ser. No. 08/828,145 filed Mar. 24, 1997 and now allowed,which claims priority to Belgian application No. 09600257 filed Mar. 22,1996, the contents of which are incorporated hereby by reference.

FIELD OF THE INVENTION

The present invention relates to compositions containing vinylidenefluoride polymers exhibiting an improved thermal stability.

It more particularly relates to such compositions containing a bismuthcarboxylate as heat stabilizer.

Technology Review

Vinylidene fluoride polymers, which are thermoplastic homopolymers andcopolymers, constitute well known polymers exhibiting an array ofadvantageous properties and, in particular, high chemical inertia andhigh resistance to ultraviolet radiation, as well as excellentmechanical strength. These polymers consequently know numerousapplications in fields, such as for example in the chemical industry,which are particularly demanding as regards resistance to corrosion. Inaddition, these polymers exhibit an excellent intrinsic thermalstability, so that they are most often employed in the absence of anyheat stabilizer.

Nevertheless, in applications in which these polymers are employed as avery thick layer, for example of the order of several tens of mm,thermal degradation can appear at the core of the material as a resultof the severe thermal conditions to which it is subjected during theshaping of thick components. Likewise, problems of thermal stabilityemerge when vinylidene fluoride polymers of very high molecular weightsare melt-shaped (for example for the shaping of articles requiring veryhigh mechanical strength) and/or when vinylidene fluoride copolymers,the intrinsic thermal stability of which is less than that of thehomopolymer, are melt-shaped. It thus proves to be currently desirableto have available heat stabilizers which are effective for vinylidenefluoride polymers.

A multitude of very diverse heat stabilizers have already been proposedfor the (essential) thermal stabilization of chlorinated polymers, suchas vinyl chloride polymers. In practice, they are most often salts oflead, calcium and/or zinc, barium and/or cadmium or alternativelyorganotins and thiotins.

Nevertheless, in Patent CH-A-275,161 of Apr. 20, 1948, a description isgiven of the thermal stabilization of vinyl chloride and vinylidenechloride polymers by the involvement of bismuth salts of highly variedorganic acids, such as, for example, bismuth formate, maleate, laurateand stearate, preference being given to the bismuth salts of fatty acidshaving at least 12 carbon atoms.

The thermal stabilization of poly(vinyl chloride) polymers by theinvolvement of bismuth salts of C₆ to C₂₂ monocarboxylic acids, such asin particular bismuth stearate and salicylate, is recommended in PatentApplication JP-A-66/19821 of Aug. 30, 1963. These bismuth salts areadvantageously employed in conjunction with heat stabilizers, such ascadmium, barium, zinc or lead salts.

SUMMARY OF THE INVENTION

The present invention is targeted at providing heat stabilizers whichare effective for vinylidene fluoride polymers.

To this end, the invention relates to compositions containing vinylidenefluoride polymers which are stabilized to heat by the involvement of aneffective amount of bismuth carboxylate, characterized in that thebismuth carboxylate is chosen from bismuth succinate, acrylate andterephthalate and their mixtures.

Excellent results are obtained with the succinate and the acrylate andtheir mixtures. A very particularly preferred bismuth carboxylate is thesuccinate.

DETAILED DESCRIPTION OF THE INVENTION

A surprising aspect of the present invention is the fact that bismuthcarboxylates described as being capable of contributing effectively tothe thermal stabilization of chlorinated polymers, and which aremoreover similar to the bismuth carboxylates employed in thecompositions according to the invention, prove to be ineffective instabilizing vinylidene fluoride polymers. Moreover, the effectiveness ofthe heat stabilizers according to the invention is such that they evenmake possible the stabilization/decoloration of thermally degraded wastevinylidene fluoride polymers.

Effective amount of bismuth carboxylate is understood to denote, for thepurposes of the present invention, an amount which is sufficient toimprove the thermal stability, that is to say to prevent the colorationof the compositions or, depending on the situation, to reduce thecoloration of the compositions (in the case of the stabilization ofwaste polymers which are already degraded) when the latter are subjectedto temperatures higher than the melting temperature of the vinylidenefluoride polymers and which are sufficient to be able to convert theminto shaped articles. This amount is not particularly critical anddepends, in particular, on the nature, on the molecular weight and, ifappropriate, on the extent of the thermal degradation of the vinylidenefluoride polymers which it is desired to stabilize. To give an idea, thebismuth carboxylate is generally employed in the proportion of at least0.05 part by weight, most often at least 0.1 part by weight and moreparticularly still at least 0.3 part by weight per 100 parts by weightof vinylidene fluoride polymer. In general, the bismuth carboxylatecontent does not exceed 5 parts by weight; most often it does not exceed3 parts by weight and more particularly still 1.5 parts by weight per100 parts by weight of vinylidene fluoride polymer.

The manufacture of the bismuth carboxylates employed in the compositionsaccording to the invention does not have a critical nature. Thecarboxylates can therefore be manufactured in any appropriate way. It ispossible, for example, to manufacture them by a wet route by reacting,in water at room temperature, stoichiometric amounts of bismuthhydroxide and carboxylic acid (succinic, acrylic or terephthalic acid ortheir mixtures), followed by filtration of the bismuth salt. It is alsopossible to manufacture them by a dry route, for example by drymixing/grinding, for a few minutes, appropriate amounts of bismuthtrioxide and the carboxylic acid (mechanochemical reactions), followedby reheating the reaction mixture to complete the reaction.

The bismuth carboxylate can be employed in any form, for example powderor aqueous dispersion. However, for reasons of convenience, it ispreferable to employ it in the form of a powder. In this case, it isadvantageous to use powders in which the particles exhibit a meandiameter of less than approximately 100 μm. The mean diameter of thebismuth carboxylate particles is preferably between approximately 0.1and 30 μm.

In addition to the bismuth carboxylate, the compositions according tothe invention can contain the usual additives for vinylidene fluoridepolymers, such as lubricating agents, pigments, additives which reducethe emission of smoke during combustion (“smoke-suppressants”), and thelike. In general, the compositions according to the invention do notcontain a heat stabilizer other than the bismuth carboxylate.

Vinylidene fluoride polymer is understood to denote, for the purposes ofthe present invention, both vinylidene fluoride homopolymers andthermoplastic copolymers of vinylidene fluoride and of ethylenicallyunsaturated comonomers, which are advantageously fluorinated, containingat least approximately 75% by weight of monomer units derived fromvinylidene fluoride The said thermoplastic copolymers advantageouslyexhibit a melting temperature at least equal to 130° C. and preferablyat least equal to 150° C. and more particularly still 165° C. Mentionmay be made, as examples of fluorinated comonomers which can be used, ofhexafluoropropylene and chlorotrifluoroethylene.

The vinylidene fluoride polymers of the compositions according to theinvention are advantageously chosen from vinylidene fluoridehomopolymers and its thermoplastic copolymers with hexafluoropropyleneor chlorotrifluoroethylene, and more particularly withchlorotrifluoroethylene. The thermoplastic copolymers of vinylidenefluoride and of hexafluoropropylene advantageously contain from 5 to 20%by weight approximately of hexafluoropropylene and more particularlystill from 8 to 15% by weight approximately. The latter particularlypreferred copolymers exhibit melting temperatures from approximately 160to approximately 135° C.

The thermoplastic copolymers of vinylidene fluoride and ofchlorotrifluoroethylene advantageously contain from 10 to 25% by weightapproximately of chlorotrifluoroethylene and more particularly stillfrom 12 to 22% by weight approximately. The latter particularlypreferred copolymers exhibit melting temperatures from approximately 170to approximately 165° C.

The vinylidene fluoride polymers which take part in the compositionsaccording to the invention can be composed without distinction of virginpolymers or of waste polymers (or alternatively of mixtures of thesepolymers).

In the case where virgin polymers are concerned, the latter are mostoften provided in the form of powders, the particles of which exhibit amean diameter from approximately 50 to 200 μm and most often fromapproximately 100 to 140 μm. In the case where waste polymers areconcerned, it is of course advisable, prior to the incorporation of thebismuth carboxylate, to grind and/or micronize the shaped articles madeof waste vinylidene fluoride polymers, for the purpose of reducing themto ground particles (ground materials) of reduced size. The wastepolymer ground materials preferably have a mean diameter not exceeding 5mm and more particularly still 2 mm.

Likewise, in the case of the thermal stabilization of thermally degradedwaste polymers, it can be advantageous, although not essential, tosubject the ground materials to a pretreatment by means of hydrogenperoxide. In this case, the incorporation of bismuth carboxylate ispreceded by a treatment of the ground materials by means of hydrogenperoxide. The said treatment advantageously takes place with stirring inan aqueous hydrogen peroxide solution, for example a 35% solution, for afew tens of minutes to a few hours, advantageously for approximately 2hours, at a temperature ranging from approximately 80 to 100° C. Afterthe treatment with hydrogen peroxide, the vinylidene fluoride polymer isfiltered, washed with water and then dried.

The preparation of the compositions according to the invention does notexhibit any particular problem. All the conventional techniques whichallow the incorporation of processing aids in thermoplastic polymers inorder to form mixtures which exist in the powder or granule form can beused. Thus, the bismuth carboxylate can be mixed with the vinylidenefluoride polymer from the polymerization stage, either by directintroduction into the polymerization mixture, at the end ofpolymerization, or alternatively by addition to the wet cake obtained bydraining or filtration of the aqueous dispersion coming frompolymerization. It is understood that this method of incorporation isonly suited to the compositions according to the invention composed ofvirgin vinylidene fluoride polymer. An advantageous procedure, which canbe used in all cases, comprises the addition of the bismuth carboxylateto the polymer, which is in the form of a powder (or of a groundmaterial), during the manufacture of a premix, at the same time as theother additives which take part in the composition. The bismuthcarboxylate can also be introduced directly into the devices where thevinylidene fluoride polymer is melted, such as screw extruders. In thiscase, the stabilized composition will exist in the form of granules(compounds).

The bismuth carboxylates employed in the compositions according to theinvention have an effectiveness such that they are suitable not only forthe manufacture of very thick components, such as slabs or rods, and forthe employment of vinylidene fluoride polymers of very high molecularweights and/or of vinylidene fluoride copolymers with a thermalstability which is lower than that of the homopolymers but also for thestabilization/decoloration of thermally degraded waste vinylidenefluoride polymers, making possible the recycling of ground materialsfrom waste articles.

The compositions according to the invention are capable of being madeuse of by all conventional techniques for the conversion of moltenthermoplastics, such as extrusion and moulding.

EXAMPLES

The following examples are intended to illustrate the invention.

Examples 1 to 4 relate to virgin compositions containing vinylidenefluoride polymers.

Examples 5 to 11 relate to thermally degraded waste compositionscontaining vinylidene fluoride polymers.

The bismuth carboxylates employed in the compositions exist as particleswith a mean diameter <30 μm.

Examples 1 to 4

In Example 1 (given by way of comparison) and in Example 2 (according tothe invention), the preparation was carried out of vinylidenefluoride/chlorotrifluoroethylene copolymer compositions containing 15%by weight of chlorotrifluoroethylene (VF2-CTFE) which have a meltingtemperature of 169° C. and a melt index (MI), measured at 230° C. undera load of 5 kg, of 15 g/10 min (ASTM D 1238). These compositions containthe following ingredients, all the parts being expressed by weight:

Ingredients Amount VF2-CTFE 100 Ca molybdate (smoke-suppressant) 0.3Polyethylene wax (lubricant) 0.2 Precipitated CaCO₃ 0.1

The composition according to Example 2 additionally contains 1 part byweight of bismuth succinate.

These compositions were mixed in a mixer of Brabender type at 270° C.with a speed of the shafts of 50 r/min and crepes were withdrawn everyfive minutes for the purpose of assessing their coloration.

After mixing for 5 minutes, the compositions according to Examples 1 and2 are still white.

After mixing for 25 minutes, the composition according to Example 1(without bismuth succinate) is brown; after 30 minutes it is black.

After mixing for 25 minutes, the composition according to Example 2 isstill white, after 30 minutes it is light beige and after 50 minutes itis still beige.

Comparison of the results of Examples 1 and 2 shows the exceptionalthermal stabilizing effect of bismuth succinate.

In Example 3 (comparative) and in Example 4 (according to theinvention), the preparation was carried out of compositions containing avinylidene fluoride homopolymer (PVDF) of high molecular weight (MI: 0.2g/10 min) and a VF2-CTFE copolymer identical to that employed inExamples 1 and 2. These compositions contain the following ingredients,all the parts being expressed by weight:

Ingredients Amount PVDF 67 VF2-CTFE 33 Polyethylene wax 0.067

The composition according to Example 4 additionally contains 1 part byweight of bismuth succinate.

These compositions were mixed at 270° C. under the same conditions as inExamples 1 and 2 and crepes were withdrawn for the purpose of assessingthe coloration.

After 10 minutes, the composition according to Example 3 is brown, after20 minutes it is blackish.

The composition according to Example 4 is still off-white after 15minutes; it is very slightly coloured (very light beige) after 20minutes and becomes brownish after 50 minutes (shade virtually identicalto that achieved by the composition according to Example 3 after 10minutes).

Comparison of the results of Examples 3 and 4 fully shows theeffectiveness of bismuth succinate.

Examples 5 to 11

In Examples 5 to 11, the preparation was carried out of compositionsfrom thermally degraded waste PVDF homopolymer originating from wastechemical engineering pipes (several years of everyday use). Therecovered pipes were ground so as to be obtain ground materials, theparticles of which exhibit a mean diameter of <2 mm.

In all these examples, except in Example 5, given by way of comparison,1 part by weight of bismuth carboxylate was incorporated (the nature ofwhich carboxylate is specified in the appended Table I).

In a first stage, the PVDF ground materials and bismuth carboxylate weremixed with stirring for 15 minutes (planetary stirrer rotating at 20r/min) These premixes were then mixed for 3 minutes at 180° C. in amixer (of Brabender type) provided with blades rotating at 32 r/min. Thecrepes thus obtained were finally pressed at 210° C. for 5 minutes in amould maintained under a pressure of 50 bars. The pressed slabs werethen examined. The colorations observed are taken up in the appendedTable I.

From the comparison of the results which appear in the appended Table I,it is evident that bismuth succinate, acrylate and terephthalatecontribute a very appreciable decoloration to thermally degraded PVDF(cf. Example 5 given by way of comparison), which reflects anappreciable improvement in its thermal stability.

The bismuth carboxylates employed in the comparative examples (Examples9, 10 and 11) are markedly less effective. In this respect, it isinteresting to compare the results of the maleate (unsaturated C₄dicarboxylate) or alternatively of the oxalate (saturated C₂dicarboxylate) with those of the succinate (saturated C₄ dicarboxylate).

TABLE No. of the Coloration of the Example Bi carboxylate pressed slab 5 (C) None brown-black  6 succinate white-beige  7 acrylate light beige 8 terephthalate light beige  9 (C) maleate dark beige-brown 10 (C)oxalate dark beige-brown 11 (C) formate dark beige-brown

What is claimed is:
 1. Compositions containing vinylidene fluoridepolymers which are stabilized to heat by an effective amount of bismuthcarboxylate, selected from the group consisting of bismuth succinate,acrylate and terephthalate and their mixtures.
 2. The compositionscontaining vinylidene fluoride polymers of claim 1, wherein the bismuthcarboxylate is selected from the group consisting of bismuth succinateand acrylate and their mixtures.
 3. The compositions containingvinylidene fluoride polymers of claim 1, wherein the bismuth carboxylateis bismuth succinate.
 4. The compositions containing vinylidene fluoridepolymers of claim 1, wherein the bismuth carboxylate is present in theproportion of a least 0.05 part by weight per 100 parts by weight of thevinylidene fluoride polymers.
 5. The compositions containing vinylidenefluoride polymers of claim 4, wherein the bismuth carboxylate contentdoes not exceed 5 parts by weight per 100 parts by weight of vinylidenefluoride polymer.
 6. The compositions containing vinylidene fluoridepolymers of claim 1, wherein the bismuth carboxylate content does notexceed 5 parts by weight per 100 parts by weight of vinylidene fluoridepolymer.
 7. The compositions containing vinylidene fluoride polymers ofclaim 4, wherein the bismuth carboxylate is present in the form of apowder.
 8. The composition containing vinylidene fluoride polymers ofclaim 5, wherein the bismuth carboxylate is present in the form of apowder.
 9. The compositions containing vinylidene fluoride polymers ofclaim 6, wherein the bismuth carboxylate is present in the form of apowder.
 10. The compositions containing vinylidene fluoride polymers ofclaim 1, wherein the bismuth carboxylate is present in the form of apowder.
 11. The compositions containing vinylidene fluoride polymers ofclaim 1, wherein the vinylidene fluoride polymers are selected from thegroup consisting of vinylidene fluoride homopolymers and theirthermoplastic copolymers with hexafluoropropylene orchlorotrifluoroethylene.
 12. The compositions containing vinylidenefluoride polymers of claim 4, wherein the vinylidene fluoride polymersare selected from the group consisting of vinylidene fluoridehomopolymers and their thermoplastic copolymers with hexafluoropropyleneor chlorotrifluoroethylene.
 13. The compositions containing vinylidenefluoride polymers of claim 6, wherein the vinylfluoride polymers areselected from the group consisting of vinylidene fluoride homopolymersand their thermoplastic copolymers with hexafluoropropylene orchlorotrifluoroethylene.
 14. The compositions containing vinylidenefluoride polymers of claim 9, wherein the vinylidene fluoride polymersare selected from the group consisting of vinylidene fluoridehomopolymers and their thermoplastic copolymers with hexafluoropropyleneor chlorotrifluoroethylene.
 15. The compositions containing vinylidenefluoride polymers of claim 10, wherein the vinylidene fluoride polymersare selected from the group consisting of vinylidene fluoridehomopolymers and their thermoplastic copolymers with hexafluoropropyleneor chlorotrifluoroethylene.
 16. The compositions containing vinylidenefluoride polymers of claim 1, wherein the vinylidene fluoride polymersare composed of virgin polymers.
 17. Compositions containing vinylidenefluoride polymers which are stabilized to heat by an effective amount ofbismuth carboxylate, selected from the group consisting of bismuthsuccinate, acrylate and terephthalate and their mixtures, wherein thebismuth carboxylate content is at least 0.05 part by weight per 100parts by weight of vinylidene fluoride polymer, and does not exceed 5parts by weight per 100 parts by weight of vinylidene fluoride polymer,and wherein the vinylidene fluoride polymers are selected from the groupconsisting of vinylidene fluoride homopolymers and their termoplasticcopolymers with hexafluoropropylene or chlorotrifluoroethylene. 18.Compositions containing vinylidene fluoride polymers which arestabilized to heat by an effective amount of bismuth carboxylate,selected from the group consisting of bismuth succinate, acrylate andterephthalate and their mixtures, wherein the bismuth carboxylatecontent is at least 0.05 part by weight per 100 parts by weight ofvinylidene fluoride polymer, and does not exceed 5 parts by weight per100 parts by weight of vinylidene fluoride polymer, wherein the bismuthcarboxylate is present in the form of a powder, and wherein thevinylidene fluoride polymers are selected from the group consisting ofvinylidene fluoride homopolymers and their thermoplastic copolymers withhexafluoropropylene or chlorotrifluoroethylene.